Multichannel optical rotary joints are often using a derotating optical element to compensate for the movement between the rotating parts. Such a derotating optical element may include a Dove prism or an Abbe-Koenig prism. In most cases light is transmitted by using optical fibers such as, for example, glass fibers or plastic fibers. For coupling the light from the optical fibers into and out of the derotating optical elements, collimators are used.
U.S. Pat. No. 5,371,814 discloses an optical rotary joint for a plurality of channels, having a Dove prism. An arrangement having a plurality of GRIN lenses is provided for coupling light into or out of glass fibers. Beam coupling is performed by several separate lenses. These lenses must be adjusted individually. A precise adjustment requires a comparatively large amount of time. Furthermore, the lenses consume a lot of space. As a result, the area to be projected, i.e. the entire surface projected via the derotating system, increases as the number of channels and the precision in adjustment increases. Therefore, a larger optical system is necessary, which also has a higher optical attenuation as a result of the longer optical paths and, at the same time, involves higher demands on the precision in adjustment.
To reduce the size of the optical system and the derotating optical element and to increase the number of channels, micro optic collimators are used. A micro optic collimator may include a fiber array and a micro lens array attached thereto.
U.S. Pat. No. 6,726,372 B1 discloses a two-dimensional micro lens array, which allows arranging of optical fibers with a high density. It includes a plurality of sticks forming conically shaped openings for holding and centering of the fibers. The disadvantage of this array is the comparatively complex assembly of a plurality of sticks that must be assembled together with high precision.
Much easier to assemble is the fiber array that has a one piece base plate, also called substrate. Such a substrate is disclosed in the German patent application DE 10304977 A1. Here, 3 flexible springs are located within each hole for centering the fiber within the hole. This allows easy assembly by simply inserting the fiber into a hole. The fiber is automatically centered therein. The disadvantages of this system are the comparatively complex shape of the substrate and the resulting high manufacturing costs.